1. Field of the Invention
The present invention relates in general to an erasable programmable read-only memory (EPROM) and method of forming the same. In particular, the present invention relates to a method of fabricating a single-poly EPROM compatible with complementary metal oxide semiconductor (CMOS) process and structure of the same.
2. Description of the Related Art
A single-poly erasable programmable read-only memory (EPROM) cell is a non-volatile storage device fabricated using process steps fully compatible with conventional single-poly CMOS fabrication process steps. As a result, single-poly EPROM cells are often embedded in CMOS logic and mixed-signal circuits.
FIGS. 1A-1C show a series of views that illustrate a conventional single-poly EPROM cell 10. FIG. 1A shows a plan view of cell 10, FIG. 1B shows a cross-section taken along line 1B—1B of FIG. 1A, while FIG. 1C shows a cross-section taken along line 1C—1C of FIG. 1A.
As shown in FIGS. 1A-1C, EPROM cell 10 includes spaced-apart source and drain regions 14 and 16, respectively, formed in a p-type semiconductor material 12, such as a well or a substrate, and a channel region 118 defined between source and drain regions 14 and 16.
As further shown in FIGS. 1A-1C, cell 10 also includes an n-well 20 formed in p-type material 12, and a field oxide region FOX formed in p-type material 12 to isolate source region 14, drain region 16, and channel region 18 from n-well 20.
In addition, cell 10 further includes adjoining p+ and n+ contact regions 22 and 24, respectively, formed in n-well 20. Current generation cells also include a p-type lightly doped drain (PLDD) region 26, which adjoins p+ contact region 22.
Further, a control gate region 28 is defined between PLDD region 26 and the field oxide region FOX that isolates n-well 20 from source region 14, drain region 16, and channel region 18. In addition, a layer of gate oxide 30 is formed over channel region 18, a layer of control gate oxide 32 is formed over control gate region 28, and a floating gate 34 is formed over gate oxide layer 30, control gate oxide layer 32, and a portion of the field oxide region FOX.
However, a cell cannot be shrunk in this type of single-poly EPROM, thus its density cannot be enhanced.